Adaptive immunity is a type of immunity that is specific to a particular pathogen and provides long-lasting protection against it. Adaptive immunity is mediated by T cells and B cells, which are both types of lymphocytes.
T cells and B cells are produced in the bone marrow and undergo maturation in the thymus and lymphoid tissues. They are capable of recognizing and responding to specific antigens, which are molecules on the surface of pathogens that elicit an immune response.
B cells are responsible for producing antibodies, which are proteins that can recognize and bind to specific antigens. When a B cell encounters an antigen that it recognizes, it undergoes clonal expansion, producing many copies of itself that secrete antibodies. The antibodies bind to the antigen and mark it for destruction by other immune cells, such as macrophages.
T cells, on the other hand, are responsible for recognizing and killing infected cells directly. There are two main types of T cells: helper T cells and cytotoxic T cells. Helper T cells produce cytokines that activate other immune cells, including B cells and cytotoxic T cells. Cytotoxic T cells recognize and kill infected cells by releasing cytotoxic granules that induce apoptosis.
Adaptive immunity is characterized by immunological memory, which allows the immune system to respond more rapidly and effectively to a pathogen that has been encountered before. This memory is maintained by long-lived lymphocytes that are specific for a particular antigen.
Vaccination is a strategy that takes advantage of adaptive immunity by exposing individuals to harmless versions of a pathogen, which elicits an immune response and provides protection against the pathogen in the future.